The hazardous and reactive nature of the gaseous emissions during ion implantation generates safety and handling challenges. Each tool discharges different types and concentrations of volatile and hazardous gases in a continuous or intermittent mode. Hydrogen, for instance, can be a byproduct of implantation. While hydrogen alone is not hazardous, there is a potential risk of ignition. Several factors can cause ignitions to occur. Such factors include the presence of an oxidizer, a specific combination of pressure and temperature, certain ratios of hydrogen and oxygen, or an ignition source.
Cryogenic vacuum pumps (cryopumps) are a type of capture pump that are often employed to evacuate gases from process chambers because they permit higher hydrogen pumping speeds. Due to the volatility of hydrogen, great care must be taken to assure that safe conditions are maintained during normal use and during maintenance of cryopumps in implanter applications. For example, cryopumped gases are retained within the pump as long as the pumping arrays are maintained at cryogenic temperatures. When the cryopump is warmed, these gases are released. It is possible that the mixtures of gases in the pump may ignite during this process. When the hydrogen vents from the pump, it can also cause a potentially explosive mixture with oxygen in the exhaust line/manifold system which is coupled to the cryopump.
A common scheme for managing safety functions in a cryopump involves a distributed system. In a typical configuration, a cryopump is networked and managed from a network terminal, which provides a standardized communication link to the host control system. Control of the cryopump's local electronics is fully integrated with the host control system. In this way, the host control system controls the safety functions of the cryopump and can regenerate and purge the cryopump in response to a dangerous situation. This feature puts the pump into a safe mode to reduce the risks of combustion. Purging the pump can dilute hydrogen gas present in the pump as the hydrogen is liberated from the pump and vented into an exhaust system.